In my prior U.S. Pat. No. 3,868,204 I have disclosed an apparatus of this description wherein the web to be cured is led in several generally horizontal passes through a stack of heated press platens forming two or more curing stages between them, the press being flanked by a pair of clamps movably disposed at opposite sides of the stack. Each clamp has as many jaws as there are platens in the stack; the clamp jaws and the press platens are substantially aligned so as to bracket the several passes of the web which is guided around one or more stationary deflection rollers positioned beyond one or both clamps as seen from the press. A preferably hydraulic actuating mechanism first closes the jaws of the clamps on the interposed web passes, then moves the clamps apart to stretch these passes and finally closes the hot platens on the stretched web portions to cure them by the applied heat and pressure. Upon subsequent reopening of the clamps and the press, the web is advanced to position previously uncured web portions between the platens.
Since the closure of the clamp jaws necessarily precedes that of the press platens, at least one of the web portions to be cured must be either raised or lowered within the clearances present between the platens of the open press so as to approach or even come into contact with one of the confronting surfaces of the associated platen pair. This results in premature exposure of certain web portions to the press heat so that curing will not be uniform throughout the web.
In many instances the press platens are provided with lateral spacing strips which limit the approach of the platens toward one another upon closure and which may be adjustable to accommodate webs of the different widths. Such adjustment may be carried out automatically, immediately before the closure stroke, by letting the web come to rest on a surface (usually the lower one) of the associated platen pair carrying these spacers while the same are separated by a distance greater than the web width. The spacers are then moved toward each other until both are contacted by the web edges whereupon the press is closed. In such a system it is particularly desirable, for the sake of uniform curing, that the deposition of the web portions on the spacer-equipped platen surfaces and the subsequent adjustment of the spacers should take place simultaneously in all curing stages.